Process for the separation of acetylene from admixture with ethylene



` D. F. BABcocK 2,250,925

Filed June 10, 1938 Puf/fied {fbg/ene SBS,

A TTQRNEY *PROCESS FOR THE SARAT-ION 0F ACETYLENE FROM ADMIXTURE WITH ETHYLENE July 29, 1941. 1

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A H 1 m S h 9e I l Daz/e f.' aoc/c INVENToR.

`PatenteclJuly 29, 19(1/1 L PROCESS FOR. THE SEPARATION OF ACETY- LENE FROM ADMIXTURE WITH ETHYL- ENE l Dale vF. Babcock, Elmhurst, Del., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application June 10, 1938, `Serial No. 212,907 2 Claims. (C11. 183-115) This invention relates to .a process for the separation of a gaseous mixture into its components and, more particularly, to a separation process involving the principle of absorption and, still more particularly, to the method of treatment of the liquors from an absorption process whereby the less soluble components are recovered essen.- tially free of the more soluble components.

Components of a gaseous mixture may be separated and recovered by scrubbing said gaseous mixture with a suitable solvent so that the more soluble components aredissolved, leaving a permanent gas essentially free from vsaid soluble components. The absorption liquor containing both the soluble components and some of the less `crude gas are adjusted so that the vapors issuing from the top of the absorber are essentially free of the more soluble components.. The liquid produced at the base of the absorber, which is essentially saturated with ,both components, is ex p vpanded into the top of ay second absorber which operates at a pressure lower than the first. The flash gases produced by this expansion, together with the other gases that are evolved in this absorber, are recompressed and f ed into the base of the high pressure absorber.' The liquid from the base of the intermediate pressure absorber is further expanded in a series of oney or more soluble permanent gasmay be further processed A closed by G. O. Curme in his U. S. Patent No.

1,422,183. Other methods of separating gaseous components, such as by gas liquefaction and rec,- tiflcation, are well known. The present process accomplishes the separation of gaseous components by a novel procedure that is much more economical than that hitherto employed. y

This invention has as its object the separation of a gaseous mixture into its components by a novel and useful process. A further object' is to accomplish this result with a minimum expenditure of power and a maximum of safety. A still further object is to separate a mixture of ethylene and acetylene into its components. Another object is to obtain a high yield of pure ethylene from a crude ethylene gas containing a' relatively small amount of acetylene. is to completely separate acetylene from a crudo ethylene gas containing a small amount of acetylene with practically no loss of ethylene. objects will appear hereinafter.

These objects are accomplished by processingv Still another object Other relative solvent power as well as absolute solvent power should be considered. The `variables,'ten^i 1 stages, with the ash gases s'o produced recompressed and passed into thevnext higher pressure absorber. The liquid produced atthe base of the lowest pressure absorber `contains essentlally all of the more soluble components originally present in the feed gas together with a small quantity of the less solublecomponents. This liquid is then boiled to expel the dissolved gases and the liquid recycled through the absorption system. The number of expansion stages selected depends upon the degree of eiliciency desired.' The greater the number of stages,- the greater the efllclency but this eiliciency is offset by the complexity of the process. For most separations, highly satisfactory results can be obtained by using three expansion stages. If the degree of purity required is nothigh or if the solvent is highly selective, two or even one stage of expansion will be sufficient. This invention may be described as, one in which the liquid` from an absorption tower is expanded to some lower pressure in one or more steps. The gas evolved during each expansion is recompressed and passed counter-current to the liquid. Inthis manner the liquid becomes depleted in the less volatile components while the gas becomes enriched in these components.

The accompanying drawing is a flow sheet diagrammatically illustrating the inyention. For simplicity, the following description of the process which refers to the drawing assumes that the crude gas -contains acetylene as its more soluble componentand ethylene as its less soluble component. Also the solvent used to absorb the acetylene is acetone, although any one' of sev' eral other solventscould have been selected for this description. y

The gas containing acetylene and ethylene was compressed to thirty atmospheres and fed into the middle of acetone absorber 4 through pipe line 2. Acetone from storage receiver I0 was pumped through pipe line 8 by means of pump i2 base of the absorber 4 through valve I4 and. conduit I8 into the top of intermediate pressure exhausting section I8. The flash gas produced in this exhausting section together with the other l gases evolved therein, passed through conduit pure acetone and pure water was prepared. The

|'I2 and compressor ||4 back into the base'of abc sorber 4. The intermediate pressureexhausting section I8 operated at approximately'lO atmospheres pressure. The heat liberated by the dissolving of the gases into the acetone in thelhigh pressure absorber 4 was abstracted using cooling coils (not shown in the attached diagram). The flow of water through the cooling coils was adjusted so that the temperature within the absorber did not rise to above 40 C. Because of the refrigerating effect produced by the dissolved gases flashing from the liquid upon expansion y through valve I4, exhausting section I8 operated somewhat below atmospheric temperature. Ihe liquid produced at the base of exhausting section I8 was expanded into the top of exhausting lsection 24 through pipe line 22 and valve 20.

This exhausting section operated at approximately 8 atmospherespressure. -'I'l'ie'vent gas-at the top of exhausting section 24 was Icompressed in compressor 28 and passed into conduit 28 into the base of exhausting section i8. 'I'he liquid at acetone passed from the still by wa'y of conduit |08 and returnedto the l acetone storage. The vent gs leaving the top of acetone absorber 4, which was washed freeof acetylene by means of the acetone, was saturated with this substance. This acetone was recovered .for further recycling to the unit by means of water scrubber 08. Water was supplied to this scrubber, which operated at 30 atmospheres, by means of pump 92. The vent gas issuing from the top, of absorber'96 through conduit 88 was essentially pure ethylene. The liquid acetone-water solution produced at the base of absorber 88 was expanded through valve |00 into the middle of acetone-water still The following is a specific example of the application of this invention.

Example to 30 atmospheres andfed into the middle of -V absorber 4 at the rate of 650 cu. ft. per hour.

'Acetone was pumped into the top of this abthe base ofy exhausting section 24'V was expanded into exhausting section 84 which operated at one atmosphere pressure. The vent gas from this exhausting'section was compressed in compressor 88 and passed through conduit 88 into the base of exhausting section 24. 'I'he liquid from the base of exhausting section 84 was passed through valve 40 and conduit 42`into outgasser No.'44. Steam was passed through the coil 48 at such' a rate that all of the gases were expelled from the acetone liquid. Essentially pure acetone liquid passed through valve 80 tothe acetone storage.4

Cooling coil 48 located near the top oi' the outgasser reduced the temperature of the vent gases issuing through conduit 52 to approximately room yThe liquid from' the base vof absorber 80 was expanded through valve 84 and conduit 88 into outlgasser 10 which was heated at the base with steam in calandria 18 and cooled at the rtop with water in condenser 1,4. its dissolved gas at the base of outgasser 10 was .passed through valve 18, -andconduit 80 back to the acetone storage system. The gas issuing from the top of 'Il via conduit 82 was essentially pure acetylene but wassaturated with acetone vapor which was removed in' water scrubber 84 Water was supplied to the top of this scrubber via conduit 88 at a sufllcient rate to remove theacetone from the vent gas which issued through conduit 80. The acetone water solution from the base of scrubber 84 passed by way of conduit 88 into the middle of the acetone water still No. 102. Calandria |08 located at the base of The acetone freed of sorber at the rate of '1.4 cu. ft. per hour. The acetylene concentration ofthe gas leaving the top of this absorber was found to be less than M00 of 1%. The gases dissolved in. the liquid at i .the .base of absorber 4 'contained approximately 90% ethylene and 10% acetylene. This liquid was expanded into exhausting section I8 and the gas from the top of this absorber was recompressed backinto the first absorber. This gasof acetylene..

Vperhour. 'I'his gas was compressed to 10 atmospheresand again scrubbed with acetone with the undissolved gases returning to the. initial absorber. 'I'he acetone liquid was then out-gassed, producing a vapor which on an acetone-free basis contained approximately 85% acetylene and 15% ethylene.

summarizing, it will be seen that the process produces an ethylene fraction containing less than %oo% of acetylene and an acetylene fraction containing in excess of 85% of this material. The volume of .the original ethylene lost with the "acetylene amounts to less than 1/4 ci' 1% of the total. If the staged expansion process had not been used, the acetylene concentration would have been but 10% vand the fraction of the tomean a. zone in which the solventvbecomesenv riched with respect to the more soluble component or components and depleted with respect to the less soluble component or compounds. This result may be accomplished by contacting the solution witha vapor which contains a higher concentration ofthe more soluble component or components than the concentration of this component or components in the vapor dissolvedin the solvent.

The composition of the gas to be processed by this invention is not limited to'that described above, nor is it limited to a mixture containing only two components. For example, the gasoline may be recovered from natural gas by this process or i! desired, thel 'carbon dioxide may be recovered from flue gases.

In order to assist the ashing of the vapors this heat is produced bythe solution of ethylene into the acetone'. Instead of cooling the absorber with water, it would be possible to saturate the acetone with ethylene and then cool the saturated liquid prior to introducing it into the high pressure absorber. Since the quantity of acetylene to be absorbed by the acetone is quite small, the temperature rise in the absorber will be greatly diminished by this preliminary saturation with ethylene. This pre-saturation of the solvent with the less soluble component prior to passing it to the absorption system is also applicable .to other absorption processes as well as the separation of C2H2 and C2114.

In the example quoted above, the relative solu- .bility of acetylene and ethylene in acetone are to produce the same results.

The use of water as a solvent is always'l attractive because of its low cost. Water is particularly attractive in this instance because of its high' solubility ratio for acetylene over ethylene (approximately 9:l) although this advantage is somewhat offset by the poor absolute solubility of acetylene in water; namely, about 1/{25 that of acetone.

If in the example described above, the absorption liquid produced at the basel of the high pressure absorber had been expanded directly to atmospheric pressure and then outgassed, the vapors would have contained but 10% acetylene, the remaining 90% being ethylene. Using the 3- stage expansion, a gas containing approximately acetylene is prepared and by `reabsorbing this gas and repeating the expansion process, an acetylene gas is produced.

It is apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof and therefore it is not intended to be limited except as indicated in the appended claims.

I claim:

1. A process for the separation vof acetylene from admixture with ethylene which comprises bringing said gaseous mixtureV into contact with a solvent having a higher solvent power lfor acetylene than for ethylene and recovering ethylene freed of acetylene as a gas, reducing the pressure on the resulting solution in at least two steps and bringing the gas evolved in each step of pressure reduction into contact with the solution-under the preceding elevated pressure, said process being further characterized in that the solvent is saturated with ethylene and the heat of solution removed` prior to contacting same with the gaseous mixture.

2. A process for the separation of acetylene from admixture with ethylene which comprises bringing said gaseous mixture into contact with acetone saturated with ethylene and recovering ethylenefreed of acetylene as a gas, reducing the pressure on the resulting solution in at least two steps and bringing the gas evolved in each step 45 of pressure reduction into contact with the solution under the preceding elevated pressure.

y DALE F. BABCOCK. 

